Under-floor heating systems are used to create heated floors in buildings. In some systems, one or more heat-radiating wires, known as “heater cables,” are disposed between a subfloor surface and a main floor surface. Once activated, the heater cables transmit heat to the main floor surface, which may then be heated to a desired temperature. To provide an effective and consistent heating area, the heater cables are arranged in a particular pattern. To that end, one or more wire retaining apparatuses may be utilized to hold the heater cables in a certain orientation and spacing to achieve a desired power output within a given area. In one approach, the wire retaining apparatus is a plurality of strips coupled together and/or attached to the subfloor (or other surface). The heater cables are coupled to the strips to maintain the heater cables in the desired orientation. Adhesive (e.g., concrete or mortar) may be poured and the main flooring may be installed on top of the heater cables such that the cables are positioned adjacent and/or are in contact with an underside of the main floor.
In another approach, a rigid or flexible underlayment may be laid on the subfloor. The underlayment includes a base that covers all of the area of the floor to be heated. An arrangement of projections extend upward from the base and, depending on the arrangement, can serve multiple purposes. First, the projections can create a primary or secondary bonding surface, such that concrete, mortar, or another adhesive contacts both the tops of the projections and the base layer exposed between the projections. This potentially improves adhesion of the adhesive as it dries or cures. Second, the projections can partially decouple the overlaying flooring from the subfloor by creating voids in the adhesive. These voids can facilitate movement of the subfloor without transmitting the movement through to the flooring. This decoupling prevents or reduces cracking (e.g., in tile or grout) and other undesired movement or effects caused by the movement of the subfloor. Third, the projections can be a partially or fully load-bearing surface, distributing loading forces across the surface area of the top and into the surrounding base as desired.
Finally, the projections can be shaped, positioned, and structurally configured to retain the heater cables within channels between the projections. In some existing implementations, the projections are spaced close enough together to hold a heater cable of a certain diameter within the channel by friction fit. In other implementations, the heater cable is placed in the channel, and then a flange is placed over the projection to extend over part or all of the channel and retain the heater cable therein. Still other implementations include flanges or recesses integrated into some or all of the projections, creating a channel which is large enough for a heater cable of a desired diameter, but which has an opening that is smaller than the heater cable; the heater cable is thus “snaked” (if the corresponding overhang over the channel is rigid) or “snapped” (if the overhang is flexible and/or resilient) into the channel.
A distinct advantage of flexible underlayments comes from manufacturing efficiencies. The base, which is typically polyethylene, is extruded as a thin sheet. The projections are stamped or thermoformed into, but can be bonded to, the base. In some implementations, a fibrous liner is bonded to the underside (i.e., opposite the projections) of the base. This liner allegedly provides additional bonding and/or decoupling properties to the underlayment in existing systems. The flexible underlayment is lightweight and can be rolled, similarly to a carpet, for easy installation.
Known underlayments have numerous drawbacks. For example, they are designed for a heater cable with a particular diameter, and it may be difficult or impossible to secure heater cables of different sizes to the underlayment because the retaining element does not grip or otherwise interact with the heater cable in a manner to secure the wire thereto. Thus, when a smaller diameter cable is used, extra care and effort is necessary to keep the cable properly tensioned so as to prevent the wire from lifting away through curling; when a larger diameter cable is used, the retaining elements (i.e., the channel, flanges, recesses, etc.) may not be flexible enough to accommodate the cable. A further drawback of some of the more versatile underlayments described in the existing art is that they have proved to be too difficult or too costly to manufacture, due to overly complicated structuring and arrangement of the projections. For example, projections that are too small or have large or abnormally-shaped flanges cannot be consistently manufactured by an efficient thermoforming process.